Step-down Voltage DC Cable
DC Input : 12V-24V, current 2A or more.
DC output: 8.4V / 8.8V
DC step-down cable length: 60cm
Compatible with:
For NIKON D3100
For NIKON D3200
For NIKON D3300
For NIKON D3400
For NIKON D5100
For NIKON D5200
For NIKON D5300
For NIKON D5500
For NIKON P7000
For NIKON P7100
For NIKON P7700
For NIKON P7800
AC adapter not included
Package include:
1 x DC Step-down Cable (input Female plug:5.5mm*2.1mm/2.5mm - output Male plug 4.0mm*1.7mm) 1 x DC coupler EP-5A (4.0mm*1.7mm)
1 x Free cable (male to male)
Compare the dc step-down cable with the USB step-up cable:
(1) The dc step-down cable can easily find an external power supply that meets the requirements and can provide a more adequate instantaneous power requirement for the camera shutter. 
(2) The USB step-up cable has high requirements for the mobile power of the USB power interface, which involves the supply voltage, the quality of the internal battery cells, and the discharge switch current of the board chip.
Tips:
General digital battery printed above parameters 7.2V / 7.4V labeled battery, it is the camera's minimum operating voltage, these batteries need to use 8.4V charger, full of power, charger 8.4V said no-load voltage, operating voltage and no-load voltage are two different concepts. External power used in the camera, You need to have enough power to supply, the camera is a load,the operating voltage is far lower than the no-load voltage.Therefore, the Camera adapter's no-load voltage is usually between 8V-9V (Note: the multimeter test is no-load voltage).